I rather got the opinion that Aeneas' conduct wasn't condoned, but was used to emphasise the force of his compulsion to follow the god's instructions about founding a new homeland for the Trojan exiles, i.e. he has to give up a very desirable woman in order to follow his destiny. In fact, Virgil piles on the tragedy pretty thickly to emphasise that point - following the will of the gods wasn't always going to be an easy path. Dido can't go with him as she is the queen - although she "abandons" everyone by killing herself so the outcome is the same anyhow. If everyone behaved rationally we wouldn't have most of the stories ever written!